Counter for load tap changing transformer



'Aug. 30,1960 R. P. MAROHN COUNTER FOR LOAD TAP CHANGING TRANSFORMER Filed Dec. 16, 1955 RESPONS/VE COUN TER ELEC THO DOcXdLM/ United States Patent COUNTER FOR LOAD TAP CHANGING TRANSFORMER Richard P. Marohn, Elm Grove, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Filed Dec. 16, 1955, Ser. No. 553,454 6 Claims. (Cl. 323-435) This invention relates in general to load tap changing transformers and in particular to improved means for recording the number of tap changes made by the transformer during a predetermined period.

' Load tap changing transformers are used extensively in the distribution of electrical power, their main purpose being to maintain the voltage of a load circuit between predetermined limits, referred to as the band width, regardless of the current drawn by the load and independently of the voltage fluctuations of the supply circuit. Most transformers usually include an exciting winding provided with a plurality of electrically spaced taps which are connected to stationary contacts of the tap changing switch. The movable contacts of the switch are usually connected to an output terminal of the transformer through an impedance device such as a reactor or preventive autotransformer to limit the flow of circu-- lating current in the exciting winding when the movable contacts are in a bridging position with respect to the stationary contacts. This usually occurs at alternate operating positions of the transformer.

It has been found desirable to provide such transformers with operational counters in order to determine the number of tap changing operations made by the switch. Besides providing information for use in servicing the mechanical parts of the switch and its actuating mechanism, information may also be obtained relative to the optimum setting for the voltage limits to be maintained at the load center by the transformer. By recording the number'of operations over a predetermined period with a predetermined band width, it is possible to determine an optimum compromise between tap changing operations. and the degree of voltage regulations desired.

The present invention provides a simple compact arrangement for recording each tap changing operation.

According to the present invention, an auxiliary winding is disposed in inductive relationship with the preventive autotransformer and is connected to an electroresponsive counter or recorder. The voltage across the preventive auto varies from substantially zero when the movable contacts are in the nonbridging position to a predetermined value when the movable contacts are in a bridging position so that the electroresponsive counter is able to record each tap changing operation.

It is therefore an object of the present invention to provide an improved operational counter for a load tap changing transformer.

A further object of the present invention is to provide a load tap changing transformer with a counter for recording the number of tap changing operations, the counter being responsive to the voltage change of the impedance device employed to limit the circulating current through the main winding of the transformer when the tap changing switch is in the bridging position.

Objects and advantages other than those mentioned above will be apparent from the following description when read in connection with the drawing in which the single figure illustrates schematically a load tap changing transformer system provided with the improved operation counter.

Referring to the drawing, there is illustrated therein a tap changing underload system comprising a supply circuit 11, a load circuit 12 and a load tap changing transformer 13 interconnecting the circuits. Load tap changing transformer 13 may be of any suitable type known in the art which employs an impedance device such as a midtap reactor or preventive auto to limit the flow of circulating current in the exciting winding of the transformer when the movable contacts are connected to diiferent taps of the exciting winding.

Load tap changing transformer 13 is preferably of the type disclosed by L. H. Hill in US. Patent 2,177,109, Voltage Regulator, issued October 24, 1939, and com prises an exciting winding 16, a series winding 17 and a dial type tap changing switch 18. The exciting winding 16 is provided with a plurality of electrically spaced taps 19, the voltage between each pair of adjacent taps being substantially equal. The tap changing switch 18 comprises a plurality of circumfcrentially spaced stationary contacts 20 which are individually connected to taps 19 of exciting winding 16. The switch 18 further includes a pair of movable contacts 21 spaced in accordance with the circumferential spacing of the stationary contacts 20 and arranged so that both contacts 2 1 may be selectively positioned on one stationary contact 20 or be positioned in a bridging relationship between adjacent stationary contacts 20.

If desired, the tap changing switch may be operated by a motor 23 which is automatically controlled in response to the voltage at some predetermined point of the load circuit 12 by a suitable control circuit 24.

In order to facilitate changing taps under load, or in other words without interrupting the flow of current to the load circuit, the system employs an impedance device 26 which asshown is connected between the movable contacts 21, and provided with a midtap to which a load terminal of the transformer 13 is connected.

When both movable contacts 21 are disposed on the same stationary contact 20, the impedance device 26 is short circuited and the terminal voltage of the transformer corresponds to the voltage of the tap. However, when movable contacts 21 are disposed in a bridging relationship with adjacent stationary contacts 20 the voltage across the impedance device 26 corresponds to the potential difference between the adjacent taps with the output voltage of the transformer corresponding to the voltage substantially midway between the adjacent taps.

It will therefore be seen that by providing an auxiliary winding 27 on the impedance device 26 and connecting winding 27 to an electroresponsive counter 28 a simple reliable means for recording the tap changing operations is obtained. Since the voltage across the auxiliary winding varies from zero to a predetermined value for successive operations regardless of the direction of the voltage change or the direction of movement of the switch, the electro-responsive counter 28 accurately records the number of tap changes. Any suitable type recording device may be employed as long as it is actuated in accordance with the voltage or current change which occurs in the auxiliary winding when the movable contacts move from a bridging position to a nonbn'dging position or vice versa.

If the tap changer is operated as a half cycling mechanism, that is where the mechanism stops alternately in the bridging and nonbridging positions, the dial of the counter would preferably be set to read in steps of two, e.g., 2, 4, 6. This is because the counter would be energized when the impedance device bridges a pair of taps and deenergized when the impedance device is in a nonbridging position.

However, if the tap changer is operated as a full cycling mechanism, that is where the mechanism stops only in the nonbridging positions, the dial of the counter would be set to read in steps of one, e.g., l, 2, 3. This is because the counter would be "energized momentarily during each switching operation. I v While only one embodiment of the present invention has been illustrated and described it will be apparent to those skilled in the art that modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims. 7

It is claimed and desired to secure by Letters Patent:

1. In a load tap changing transformer having a tapped winding and a tap changing switch for selectively connecting an output terminal of said transformer to various taps on said exciting winding through a preventive autotransformer connected between a pair of movable contacts of said switch, the improvement comprising means for recording the number of operations of said switch including an auxiliary winding inductively related to said autotransformer, and an electromagnetic counter responsive to the voltage changes in said auxiliary winding resulting from said switching operations.

2. A load tap changing transformer comprising in combination a winding having a plurality of taps, a tap changing switch having a plurality of stationary contacts connected to said taps and at least one pair of movable contacts cooperating with said stationary contacts to vary the output voltage of said transformer in steps, impedance means connected between said movable contacts to limit the flow of circulating current through said exciting Winding when said movable contacts are disposed in a bridging relationship with said stationary contacts, an auxiliary winding inductively related with said impedance means, and a counting device operable in response to the voltage induced in said auxiliary winding when said movable contacts are in said bridging relationship.

3. A tap changing under load transformer comprising in combination a winding having a plurality of taps, a tap changing switch having a plurality of electrically spaced contacts the potential difference between any two adjacent contacts being substantially equal, and a pair of movable contacts adapted to be moved with respect to said stationary contacts to vary the output voltage of said transformer, a preventive autotransformer for limiting the flow of circulating current through said winding when said movable contacts are in a bridging position with respect to said stationary contacts, means connecting said preventive autotransformer between said movable contacts, auxiliary winding means inductively related to said preat ventive autotransformer, and means operable in accord ance with the voltage induced in said auxiliary winding means by the change in voltage across said preventive autotransformer to record the number of tap changes made by said transformer.

4. A tap changing under load transformer comprising in combination a winding having a plurality of taps, a tap changing switch having a plurality of electrically spaced contacts the potential difference between any two adjacent contacts being substantially equal, and a pair of movable contacts adapted to be moved with respect to said stationary contacts to vary the output voltage of said transformer, a reactor having a main winding connected between said movable contacts and an auxiliary winding inductively related to said main winding, a voltage responsive counting device for recording the number of tap changes made by said transformer, and means connecting said auxiliary winding to said device to cause said device to register in response to the change in voltage in said auxiliary winding.

5. In a load tap changing transformer having an impedance device connected intermediate two tap changing contacts that are movable through a sequence of tap switch positions, a first predetermined voltage condition existing between said contacts at alternate of said positions and a second predetermined voltage condition existing between said contacts at the other of said positions, the improvement comprising a counter difierently responsive to said first and second voltage conditions and means coupling said counter with said impedance device for advancing said counter in response to one of said voltage conditions between said contacts to record the number of tap changes.

6. In a load tap changing transformer having an impedance device connecting two top changing contacts that are movable through a sequence of tap switch positions, a first predetermined voltage existing across said impedance device at alternate of said positions and a second predetermined voltage existing across said impedance device at the other of said positions, the improvement comprising a counter differently responsive to said first and second voltages and means coupling said counter with said impedance device for advancing said counter in response to one of said voltages to record the number of tap changes.

References Cited in the file of this patent UNITED STATES PATENTS 

